1. Field of the Invention
This invention relates to non-crystalline semiconductor solar batteries and methods of manufacture thereof; more particularly, the batteries are non-crystalline semiconductor solar cells of the type including (1) a transparent conductive film formed on an insulated transparent substrate, with the transparent conductive film defining a first electrode, (2) a non-crystalline semiconductor film formed on the transparent conductive film, and (3) a metal film formed on the non-crystalline semiconductor film, with the metal film defining a second electrode.
2. Discussion of the Prior Art
Recently, a type of non-crystalline semiconductor solar battery has become well known as a low cost solar battery, in which photo-electric conversion is carried out by a non-crystalline silicon (hereinafter referred to as "a-Si," when applicable) film which is made from mono-silane or the like, by plasma chemical vapor deposition (CVD). The non-crystalline semiconductor solar battery can be formed to have a large area and therefore it is expected that it will be used for electric power generation.
FIG. 2 shows the structure of one example of an a-Si solar battery. The solar battery comprises an insulated transparent substrate, namely, a glass substrate 1, a transparent conductive film 2 of SnO.sub.2 or ITO (indium tin oxide) formed on glass substrate 1, an a-Si film 3 having a pin junction formed on transparent conductive film 2, and a metal film 4 formed on a-Si film 3. If, in the formation of a-Si film 3, the a-Si does not sufficiently adhere to transparent conductive film 2, pinholes 5 are formed. It is theorized that the a-Si does not sufficiently adhere to transparent conductive film 2 because of the surface condition or smudges of transparent conductive film 2. In manufacturing large-area solar batteries, the probability of formation of pinholes 5 is high. When the metal film formed on a-Si film 3 enters pinholes 5, the metal film 4 is electrically connected to the transparent conductive film 2, as a result of which the characteristic of the solar battery is lowered and the manufacturing yield of the solar battery is decreased correspondingly. In order to overcome the above-described difficulty, a method has been developed, as disclosed in Japanese Patent Application No. 77263/1973 (open for public inspection), in which, after a-Si film 3 has been formed, pinholes 5 are filled with insulating material. However, filling pinholes 5 with insulating material is troublesome and increases the manufacturing cost. In another method developed to overcome the above-described difficulty, a photo-etching technique is utilized to coat a-Si film 3 with photo-resist, and the photo-resist, except for that in pinholes 5, is removed by exposing and developing. However, this latter method is still disadvantageous in that a-Si film 3 may be damaged when the resist layer is peeled off the a-Si film 3 and also the metal film does not sufficiently adhere to the a-Si film because of the resist residue remaining on the film.